In the current technical evolvement towards the NGN (Next Generation Network) technology, it is already possible to realize the communication of multimedia information such as voice, video, etc. over a packet network such as an IP network or a traditional telephone switching network such as a PSTN by various means such as Softswitch, H.323, etc.
Especially in a packet network such as an IP network, due to there being various networking methods such as WAN, LAN etc., in implementing the intercommunication of multimedia information, the situation where devices such as media gateways and IP telephones in a public network and a private network or in private networks intercommunicate will occur.
Since a private network address cannot be used in a public network, how to translate a private network address into a public network address, and how to find the public network address of the destination and the corresponding private network address is the key to solve this problem.
In the existing IP technology, a common method is to use the NAT (Network Address Translation) protocol. The NAT protocol can associate the private network address of a device in each private network with a corresponding public network address in advance, and when the device needs to communicate with a device such as a media gateway or IP telephone in another network, all the IP packets containing the signaling traffic and media traffic messages sent out will have the private network address replaced by the corresponding public network address using the NAT protocol in a special device and then be forwarded. Because on both the calling and called sides, the address has been translated into the public network address using the NAT protocol, any existing mature routing protocol can be used to find the called side, realizing the voice, video communication. The biggest advantage of this method is its simpleness, but its shortcomings are also especially obvious:                A big reason for using private network addresses is the shortage of public network address resources; while in view of the characteristics of implementing a packet-based (e.g., IP) voice, video and other calling service, adopting the NAT method will consume a large amount of address resources. This is because, firstly, each device will be pre-allocated a public network address to associate with a private network address; when this device is not online at all, this association still exists, and cannot be allocated dynamically. Secondly, a device such as a media gateway or IP telephone needs a port for call signaling exchanges during call establishment, and once the call is established, it needs other ports for the transmission of media traffic such as voice, video, etc; using the NAT protocol, one can only establish in advance the associations between these private network ports and the corresponding addresses and ports of the public network. Accordingly, even when the device such as a media gateway or IP telephone etc is not in use, these ports for media traffic must remain associated, thus wasting the address resources.        In the message exchanges between devices such as media gateways or IP telephones etc. and their call controllers (e.g., a Softswitch, a GateKeeper in H.323, etc.), various signaling protocols, such as H.248, MGCP, SIP, H.323, etc., are widely used, which carry the address information of the media traffic of the calling and called sides in the capability negotiation. Whereas the NAT protocol can only translate an address in an IP packet header, and does not intervene in the content of the protocol payload in the IP packet, therefore these addresses of the media traffic (which are still private network addresses) cannot be translated; consequently, the media traffic will not be conveyed and thus fail. This is the most essential weakness of using the NAT scheme.        
To address the above shortcomings of the NAT scheme, now there also appeared other improved solutions, such as the protocol analysis gateway:                A device such as a media gateway or IP telephone etc. in a private network does not send signaling messages directly to a call controller (e.g. a Softswitch, GateKeeper, etc.), but first sends these messages to a protocol analysis gateway, which can associate them to a public network address according to their private network address statically or dynamically, and then forward them the call controller (a Softswitch, GateKeeper, etc.). Similarly, the media traffic is also associated to a public network address dynamically, thus realizing the exchange of the media traffic.        The biggest advantage of this scheme is that the protocol analysis gateway not only translates between a public network address and a private network address, but also, for each protocol, translates the private network address relating to the media traffic in the protocol into a public network address. For example, for a H.248, MGCP, or SIP protocol, the SDP therein can be analyzed, and the private network address therein can be extracted and replaced.        
This scheme, however, has its own disadvantages:                Since a device such as a media gateway or IP telephone in a private network does not send commands directly to the call controller, the realization of some functions (e.g., switching, access authentication, and mobility etc.) may be affected; and at the same time, for such a call controller, it manages the public network address to which a protocol analysis gateway corresponds, but cannot manage a device such as a media gateway or IP telephone etc. in an actual private network, which may also affect the realization of some functions (e.g., network topology, location, etc.).        Since a device such as a media gateway or IP telephone etc. in a private network does not send commands directly to the call controller, when moved into another private network, it will find difficulty in collaborating with the new protocol analysis gateway.        This scheme affects the integrity of the IP packet payloads by engaging in analyzing and changing the signaling contents. In particular, if these IP packets use security features, such as encryption, the address replacement may not be able to be realized at all.        This scheme requires each protocol to have its own protocol analysis gateway, and with the number of protocols used by the devices such as media gateways or IP telephones etc. in a private network increasing, the number of protocol analysis gateways also increases.        The consequence of this scheme is that even the call from a device in the same private network will be forwarded via the protocol analysis gateway, as a result, on the one hand, the forwarding of the media traffic increases the processing volume of the protocol analysis gateway; on the other hand, the voice quality of the device will be affected.        
To search for relevant existing patents, we queried in the web page of the State Intellectual Property Office of the P.R.C. with “IP” as the keyword, and found on relevant patent document (by 2003/Mar./24).
Using “private network” as the keyword in the abstract field to retrieve abstracts, there was a relevant patent:                An invention patent application, Chinese Patent Application No. 01135610.3 (Publication No. CN 1411220A), entitled “Method and system for implementing the IP voice service in a private network”.        
This patent application, submitted by Huawei Technologies, describes a method that when a terminal in a private network registers with a VoIP server, translating the private network addresses of all the signaling channels and media channels required by the calls into the corresponding public network addresses using the NAT protocol, and maintaining the possession of these channels all the time.
It is essentially different from the present invention in the implementation concept.
1) It belongs to the NAT implementation method, whose advantages and disadvantages can be seen in the above description of the background technology, and when using the technique of this patent application, there is the disadvantage of possessing a large amount of NAT public network addresses even when no call is made and thus wasting resources. Therefore, this method can have much fewer connected users than the present invention with the same address translation capability. In other words, its efficiency is not high.
2) To remedy the shortcoming that in the NAT protocol only an IP address and not the signaling content can be modified, the technique of this patent application extends the standard VoIP protocols (by which is meant the MGCP protocol in the patent application), making “the VoIP server send the public network address and port number of the corresponding logic channel to a PC client in the response message to a login request of the PC client of a private network user. This belongs to the modification of a standard protocol, the starting point of which is vastly different from the present invention.
3) According to this patent application, even the voice communication between users in the same private network must goes around through the public network, which will increase the voice delay, causing the degradation of the voice quality, and lower the security of the internal communication.
4) In this patent application, there is no description of the case where a private network is nested within another private network, but judging from what its content relates to, it is possible to realized a private network being nested within another private network, but many important links, such as the coupling of the address proxy server and the VoIP, the workings of the gateway, etc., need to be described and disclosed explicitly.
Querying at http://www.uspto.gov by using keywords (((“PRIVATE NETWORK” OR NAT) AND “IP ADDRESS”) AND TELECOMMUNICATION), about 93 patents (by 2003/Mar./24) could be found, the majority of which are irrelevant to the present invention, and the relevant patents are as follows:                U.S. Pat. No. 6,526,056, entitled “Virtual private network employing tag-implemented egress-channel selection”.        
This patent, submitted by CISCO, identifies different VPNs (Virtual Private Network) with TAGs; it encapsulates a TAG according to the destination VPN at an edge router of a VPN (this TAG was negotiated by two VPN edge routers), and then achieves the objective of crossing a private network boundary by adding the TAG at the sending side when sending the data and removing the TAG at the receiving side. It is relevant to but not in conflict with the present invention. Since it uses edge routers to negotiate and determine the TAG values, without a call controller to coordinate and manage the TAG values in the entire domain, it does not constitute a system for implementing multimedia calls across a private network boundary, and will face difficulties in particular when implementing a complex networking method (e.g., the case where a private network is nested within another private network) for multimedia calls. What this U.S. patent describes is equivalent to a method implemented by the boundary gateway (BGW) of the present invention.                U.S. Pat. No. 6,523,068, entitled “Method for encapsulating and transmitting a message includes private and forwarding network addresses with payload to an end of a tunneling association”.        
This patent, submitted by 3Com, is used for packaging a packet before it is sent from a private network, and then sending it through a tunnel; and identifying the packet after receiving it in a public network. The concept of this patent is related to an implementation method of the system presented by the present invention, and similar to the above patent, it describes specifically a method for sending a packet from a private network to a public network, and not the whole system. This is where it differs from the present invention, which describes a system that, in addition to this aspect, further has other aspects concerning how to establish a connection between private networks in order to make multimedia calls.                U.S. Pat. No. 6,496,867, entitled “System and method to negotiate private network addresses for initiating tunneling associations through private and/or public networks”.        
It is also submitted by 3Com, and similar to the U.S. Pat. No. 6,523,068, presents a system and method for establishing a tunnel between a public network and a private network—it negotiates the public network addresses of the source and destination private network devices through a third party device and edge devices. It is closest to the system described in the present invention, both of them crossing a private network boundary through tunneling, but the core ideas in their implementation are quite different.
1) In this patent, the role of the third party device is only to obtain the public network address of the destination, and it only negotiates the IP addresses of the source and destination edge devices in the same network, that is, it is segment-to-segment; while the present invention aims to be end-to-end, which is much simpler in terms of device usage and technical complexity. In multimedia calls, such a method of segment-to-segment public network address negotiation will make the call control method complicated and dispersed, and difficult to realize some service logics.
2) In this patent, what is described throughout is the cross-private network boundary communication between two different subnetworks in a public network, wherein the source end edge device (equivalent to the boundary gateway in the present invention) stores the address tables of the private network addresses of source end devices, the public network addresses of destination end edge devices, and the private network addresses of destination end devices, whereby the routing is determined. If it is the case where a private network is nested within another private network, then inferring from its discussion, since the source end edge device cannot obtain directly the private network address of the destination end device (because there are multiple private networks in between and there are multiple edge devices), finding the routing by using the method of this patent will fail, unless it adds more identifiers to identify this tunnel. The present invention, since using other methods, has no such problem, and can realize the networking situation where a private network is nested within another private network.
3) In this patent, the core of its method is to hope the communication between the source end device and the destination end device is like that within the same network. Therefore, it dynamizes the IP address allocation of the source and destination end devices, and then, when initiating the communication, by means of transferring the private network addresses or selecting from multiple private network addresses, selects the private network addresses of the source and destination end as the IP addresses of the same network, and at the same time ensures that these addresses do not duplicate in their respective networks. Thus, when data traffic of either end is sent to the opposite end, it will be transferred first to the corresponding edge device (because the destination address is not in the same private network), and then through the corresponding address table inside the edge device, the edge device of the opposite end is found, and then the device of the opposite end is found, thus completing the data exchange. The benefits are obvious, but the biggest problem is that, since the transfer of the private network addresses affected the IP address allocation plan of the devices in the destination private network, some services of the devices in the destination private network unrelated to the communication with the source end devices may be affected to not function normally; since the IP address has been allocated as an address in the same network of the source side, if at the same time the service needs to browse the Web, it may for the reason of the IP address, for the service is one unrelated to the source end. Secondly, since private network addresses are to be transferred, the private network addresses of the source and destination end must be planned as in the same network, even when they are not in communication. This is feasible for some applications (e.g., the communication between a company headquarters and its branches in various regions), but for the communication between different companies, even between different operators, this requirement is too demanding. Thirdly, the transfer of private network addresses may bring security threats to the destination end devices. In contrast, the present invention has no requirement on IP address planning, and will not damage the IP address plan of the destination end; therefore its applicable range is much wider than this patent.                U.S. Pat. No. 6,006,272, entitled “Method for network address translation”.        
What it presents is that: devices in each private network need to be configured with a private network address, the corresponding public network address, and a MAC address; a router determines whether it is a public network or a private network based on the destination address, and then performs address translation. This patent only relates to the NAT, and is similar to the NAT translation as described above, whose advantages and disadvantages have also been described above.
In the foregoing, the technical characteristics and deficiencies of various prior art solutions have been described in detail, and it is obvious the prior art techniques need to be improved.